Abstract/Summary

It has repeatedly been shown that increased nitrogen (N) deposition results in dramatic
shifts in vegetation composition. The sources of N-deposition vary from agriculture
(mainly NH3 and NH4) to industry and traffic (mainly NOx).
Effects of these different N forms on the vegetation and biogeochemistry of an
ombrotrophic peat bog, Whim Moss (~15km southwest of Edinburgh), have been
investigated since April 2002, by employing an automate N manipulation system. This
field experiment, uniquely, offers the possibility to investigate the effects of the different N
forms at the same site and at application rates and deposition scenarios simulating
natural variation in rainfall. Within the manipulation system there are two N manipulations:
Dry, where gaseous NH3 is released over a 60 m transect at concentrations that simulate
a 100,000 bird poultry unit (0.4-200 μg m-3), and Wet, as soluble nitrate or ammonium,
covering the full range of UK wet N-deposition (8 – 64 kg N ha-1yr-1).
The effects of dry N deposition on the vegetation and biogeochemistry at different
distances from the NH3 source have been analysed. In the wet N deposition experiment, 5
treatments were followed, ranging from 8-64 kg N ha-1yr-1 and differing in N form as either
oxidised or reduced N.
Samples of soil water were obtained using mini-rhizon samplers and were tested for pH,
NH4, NO3, P and base cations. Young (1 year old) shoots of Calluna vulgaris L. (Hull),
Erica tetralix L. and Sphagnum capillifolium Ehrh. (Hedw.) were harvested and tested for
chlorophyll concentrations, aminoacids and P and base cation concentrations in acid
digests.
The preliminary results show differences between treatment N forms and N doses and
along the NH3 gradient. In this presentation we will focus on the plant responses to the
changes in the biochemistry.
CAPER Conference